1. Field of the Invention
The present invention relates to a piezoelectric resonator and a piezoelectric resonator part.
2. Description of the Related Art
The piezoelectric resonators using piezoelectric ceramics have widely been employed as filters, resonators or sensors. In particular, piezoelectric materials such as lead titanate (PT) or lead zirconate titanate (PZT) are cheaper than piezoelectric single crystal materials. Therefore these piezoelectric ceramics have been widely used as resonators for generating basic clock signals in reproduction apparatus of recording media as CD-ROM (Compact Disc-Read Only Memory) or DVD (Digital Versatile Disc). However, since these piezoelectric materials contain lead (Pb), it has been demanded to develop a piezoelectric material without containing lead for less environmental impact.
Known piezoelectric materials without containing lead include, for example, compounds having perovskite structure and solid solutions thereof such as tantalate compounds or niobate compounds and, ilmenite structure compounds and solid solutions thereof, bismuth layer compounds, or compounds having the tungstenxe2x80x94bronze structure. Of these substances, the bismuth layer compounds have excellent properties, so that dielectric constant is low, piezoelectricity is relatively large, mechanical quality coefficient, Qm, is high and the Curie temperature is high, so that this compound deteriorates less at high temperature.
However, the effective Poisson""s ratio of these piezoelectric materials is less than 1/3. Consequently, the fundamental thickness extensional wave vibration could not be used in energy trapping. Utilization of the fundamental wave was difficult in a structure similar to that of the piezoelectric resonator using the piezoelectric material of the effective Poisson""s ratio being 1/3 or higher such as PZT, for example, in a structure where a pair of opposite faces of the piezoelectric substrate are furnished with a pair of electrodes having smaller areas than the area of the piezoelectric substrate. In the piezoelectric resonator using these piezoelectric materials, there are many piezoelectric resonators suppressing vibrations of the fundamental waves and utilizing tertiary harmonics in the thickness extensional vibration.
However, with respect to a resonance sharpness value, Q, indicating easy occurrence of vibration in a specific wavelength, as the tertiary harmonic wave was smaller than the fundamental wave, there was a problem in utilizing the tertiary harmonics. The vibration of the fundamental wave having a large Q was suppressed by damping and the vibration of the tertiary harmonics having a small Q was used by necessity so a stable vibration could not be obtained. Thus, although the piezoelectric material not containing lead has been in demand, a general practice has been difficult.
Further, it is generally known that the piezoelectric resonating part utilizes a piezoelectric vibrator as a resonator for obtaining an oscillation frequency. The piezoelectric vibrator is formed with a piezoelectric element with a pair of opposing electrodes located on either side thereof. The piezoelectric vibrator is laminated onto a capacitor element in a manner that one side surfaces located in the thickness direction are positioned opposite to each other, the capacitor element having two load capacities formed thereon. Further, connecting conductors are provided to electrically and mechanically connect input electrodes, output electrodes and ground electrodes. A cap is provided to seal the piezoelectric resonating part.
Such a piezoelectric resonating part is disclosed, for example, in JP-A-60-123120, JP-A-1-236715, JP-A-8-237066 or JP-A-10-135215 and others.
As the piezoelectric resonating part utilizing thickness extensional vibration mode, one is generally known utilizing a fundamental wave vibration mode and another one is known utilizing a harmonic vibration mode, in particular a tertiary harmonic vibration mode.
The typical example of piezoelectric resonating part utilizing the tertiary harmonic vibration mode is of a type for energy trapping. The piezoelectric resonating part of this type includes the piezoelectric substrate having some non-vibrating portions. With these portions being fixed and supported, it is possible to obtain the piezoelectric resonating part which is free of property deterioration and may be widely utilized.
The piezoelectric resonating part in the thickness extensional vibration mode utilizes the fundamental wave vibration. It may, therefore, obtain a high Q max resonant property. However, in contrast to the energy trapping type, it has difficulty in obtaining the non-vibrating portions. Especially in the case when the piezoelectric resonating part is made small-sized, the piezoelectric substrate itself will vibrate, and this will make it impossible to fix and support to the piezoelectric substrate.
Since the piezoelectric resonating part utilizes the fundamental wave vibration mode, when the piezoelectric is mounted onto the dielectric substrate, a viscosity change of electrically conductive paste at the time of connection will occur. This will cause the connection areas to be uneven, and the paste will often spread out, making the adhesion strength unstable. Accordingly, the suppression of vibration energy by the piezoelectric resonating part will cause deterioration of the resonant property, and failure of complete suppression of the unnecessary vibration will further deteriorate the resonant property. Thus, the piezoelectric resonating part will often fail to produce stabilized oscillation which is, for example, free of skipped oscillation and others.
It is an object of the present invention to provide a piezoelectric resonator by using the piezoelectric material with the effective Poisson""s ratio being less than 1/3, enabling it easy to obtain stable vibration.
It is another object of the invention to provide a piezoelectric resonating part capable of preventing the attenuation of vibration energy to minimum and supporting the piezoelectric resonator under a stabilized condition.
According to a first aspect of the present invention, a piezoelectric resonator comprises a piezoelectric substrate containing a piezoelectric material of an effective Poisson""s ratio being less than 1/3. This piezoelectric substrate having a pair of opposite faces; a pair of corresponding electrodes on said opposite faces; wherein the opposite faces of the piezoelectric substrate are rectangular; and the sum of the length of one side of the face and the length of the other perpendicular side of the same face is limited within the range from 2.22 to 2.24 mm or the range from 2.34 to 2.48 mm.
In the piezoelectric resonator according to the first aspect of the present invention, since the sum of the length of one side of the face and the length of the other perpendicular side of the same face is limited within the range from 2.22 to 2.24 mm or the range from 2.34 to 2.48 mm, it is possible to make use of the vibration of the fundamental wave, and stable vibration is available.
In the piezoelectric resonator it is preferable that, for example, the respective lengths of one of the sides of these opposite faces of the piezoelectric substrate are within the range from 1.06 to 1.24 mm, and the respective lengths of the perpendicular sides are within the range from 1.16 to 1.30 mm. It is more preferable that the respective lengths of one of the sides of the opposite faces are limited within range from 1.16 to 1.22 mm, and respective lengths of the perpendicular sides are limited within range from 1.18 to 1.22 mm. Further, it is preferable that the piezoelectric substrate is composed to include the bismuth layer structure containing bismuth-strontium-titanium-oxygen. The compound of the bismuth layer structure may contain lanthanum.
According to a second aspect of the present invention, a piezoelectric resonator comprises a piezoelectric substrate containing a piezoelectric material of an effective Poisson""s ratio being less than 1/3. This piezoelectric substrate having a pair of opposite faces; a pair of corresponding electrodes on said opposite faces; wherein respective areas of the opposite faces of the piezoelectric substrate are, with respect to the one side, from 1.22 to 1.26 mm2 or from 1.35 to 1.538 mm2.
In the piezoelectric resonator according to the second aspect, since the respective areas of the opposite faces of the piezoelectric substrate are, with respect to the one side, from 1.22 to 1.26 mm2 or from 1.35 to 1.538 mm2, it is possible to make use of the vibration of the fundamental wave, and stable vibration is available.
In the piezoelectric resonator of the second aspect, it is preferable that the piezoelectric substrate has a bismuth layer compound structure, for example, bismuth-strontium-titanium-oxygen.
A piezoelectric resonator according to a third aspect of the present invention comprises a piezoelectric substrate containing a piezoelectric material of an effective Poisson""s ratio being less than 1/3. This piezoelectric substrate having a pair of opposite faces; a pair of corresponding electrodes on said opposite faces; wherein the opposite faces of the piezoelectric substrate are rectangular; a length of one side of the opposite face is limited within 5 times or less of the thickness of the piezoelectric substrate; and a length of the other side perpendicular with said one side of the opposite face is limited within the range from 0.93 times to 1.07 times of the length of the one side.
In this piezoelectric resonator according to the third aspect, the length of the one side of the opposite face is limited within 5 times or less of the thickness of the piezoelectric substrate, and a length of the other side perpendicular with said one side of the opposite face is limited within 0.93 times to 1.07 times of the length of the one side. Accordingly, even if a piezoelectric material of the effective Poisson""s ratio being less 1/3 is used, it is possible to make use of the vibration of the fundamental wave, and stable vibration is available.
In the piezoelectric resonator according to the third aspect, it is preferable that the area of the vibrating electrode is 6% or more of the area of the opposite face. Preferably, the piezoelectric substrate is a bismuth layer compound, for example, bismuth-strontium (Sr)-titanium (Ti)-oxygen (O), and further the piezoelectric substrate may be composed to include lanthanum (La) and manganese (Mn).
A piezoelectric resonating part according to a fourth aspect of the present invention comprises a piezoelectric resonator, a substrate and connecting conductors. The piezoelectric resonator is operated in thickness extensional vibration mode and has two side electrodes. The two side electrodes are provided at opposite sides of the piezoelectric resonator which are different from the sides located in the thickness direction, and are conducted to vibration electrodes respectively. The substrate has terminal electrodes provided at the surface thereof. The connecting conductors include metal balls which are located between the side electrodes of the piezoelectric resonator and the terminal electrodes of the substrate and are fixed to connect the two members.
As described above, in the piezoelectric resonating part according to the fourth aspect of the invention, the piezoelectric resonator has two side electrodes provided at opposite sides thereof which are other than the sides located in the thickness direction thereof, and connected to vibration electrodes respectively. Therefore, electric energy may be supplied to the side electrodes to excite the piezoelectric resonator.
With the functions as described above, there may be realized the piezoelectric resonating part which will produce a stabilized resonating property of high Q max representing the value of resonation property while eliminating radiation of vibration energy, incomplete suppression of unnecessary oscillation, deterioration of resonating property and inferior oscillation including unstable skipped oscillation and others.